Chapter LXIX: Section XXIV: Now the first broad characteristic of the building, and

the root nearly of every other important peculiarity in it, is its confessed _incrustation_. It is the purest example in Italy of the great school of architecture in which the ruling principle is the incrustation of brick with more precious materials; and it is necessary before we proceed to criticise any one of its arrangements, that the reader should carefully consider the principles which are likely to have influenced, or might legitimately influence, the architects of such a school, as distinguished from those whose designs are to be executed in massive materials.

It is true, that among different nations, and at different times, we may find examples of every sort and degree of incrustation, from the mere setting of the larger and more compact stones by preference at the outside of the wall, to the miserable construction of that modern brick cornice, with its coating of cement, which, but the other day, in London, killed its unhappy workmen in its fall. [Footnote: Vide "Builder," for October, 1851.] But just as it is perfectly possible to have a clear idea of the opposing characteristics of two different species of plants or animals, though between the two there are varieties which it is difficult to assign either to the one or the other, so the reader may fix decisively in his mind the legitimate characteristics of the incrusted and the massive styles, though between the two there are varieties which confessedly unite the attributes of both. For instance, in many Roman remains, built of blocks of tufa and incrusted with marble, we have a style, which, though truly solid, possesses some of the attributes of incrustation; and in the Cathedral of Florence, built of brick and coated with marble, the marble facing is so firmly and exquisitely set, that the building, though in reality incrusted, assumes the attributes of solidity. But these intermediate examples need not in the least confuse our generally distinct ideas of the two families of buildings: the one in which the substance is alike throughout, and the forms and conditions of the ornament assume or prove that it is so, as in the best Greek buildings, and for the most part in our early Norman and Gothic; and the other, in which the substance is of two kinds, one internal, the other external, and the system of decoration is founded on this duplicity, as pre-eminently in St. Mark's.